A conversion element in which a non-single crystalline semiconductor such as hydrogenated amorphous silicon (hereinafter abbreviated to a-Si) is used is well known as the conversion element which converts the radiation including the light such as the visible light, the infrared ray, the X-ray, the alpha ray, the beta ray and the gamma ray into the electric signal. A radiation detecting apparatus in which a flat panel detector (hereinafter abbreviated to FPD) is used receives attention as the radiation detecting apparatus in which the conversion element is used. In FPD, plural pixels are arranged in a two-dimensional matrix. The pixel includes a conversion element prepared by a non-single crystalline semiconductor on an insulating substrate and a switching element such as a thin film transistor (hereinafter abbreviated to TFT) prepared by the non-single crystalline semiconductor. In FPD, the conversion element converts the radiation having image information into a charge while a predetermined bias is applied to the conversion element, and the electric signal based on the image information can be obtained by reading the charge with the switching element. For the conversion element made of the non-single crystalline semiconductor, sometimes long-time bias application to the conversion element induces degradation of sensor characteristics. Therefore, there is an attempt that the degradation of sensor characteristics is reduced due to the long-time use by applying a zero-potential bias to the conversion element except in taking the image while applying a predetermined bias to the conversion element only in taking the image. However, when the predetermined bias is applied to the conversion element only in taking the image, unnecessary current is generated by the charge and the like trapped by a defect energy level in the non-single crystalline semiconductor, and sometimes sensitivity which is of a signal-to-noise ratio is decreased due to the noise caused by the unnecessary current. The unnecessary current generated by the charge trapped by the defect energy level is an intrinsic problem of the non-single crystalline semiconductor.
It is possible that the decrease in sensitivity caused by the unnecessary current is reduced by providing a standby period during which the signal is not read from the conversion element for a given interval after the predetermined bias is applied to the conversion element. However, from the viewpoint of immediacy, it is necessary to improve the standby period in the actual apparatus operation, because the standby period during which the signal is not read from the conversion element is provided.
Therefore, as disclosed in US Patent Publication No. 2002/0024016, there is well known a drive method and an apparatus, in which the photoelectric conversion element which is of the conversion element made of a-Si is irradiated with the light not having the image information before the radiation, and thereby the conversion element can take the image immediately after the predetermined bias is applied to the conversion element. The apparatus disclosed in the US Patent Publication No. 2002/0024016 has a structure in which a light source for emitting the light not having the image information is arranged on the backside of the substrate in which the photoelectric conversion element is provided, the light from the light source is transmitted through the photoelectric conversion element or between the pixels, and the light is accepted by a light acceptance surface of the photoelectric conversion element. US Patent Publication No. 2002/0014592 also discloses a similar configuration.
The improvement of the sensitivity, i.e., the improvement of output and the noise reduction are always demanded in the photoelectric conversion element. Specifically, the improvement of a numerical aperture which is of an occupied area ratio of the conversion element in one pixel can be cited as an example of the improvement of the output. On the other hand, the reduction of interconnection resistance, i.e., the increase in width of each interconnection can be cited as an example of the noise reduction. That is, in order to obtain the high-performance radiation detecting apparatus, it is necessary that the increase in interconnection width and the improvement of the numerical aperture be simultaneously achieved.
Therefore, there is thought a method in which the numerical aperture is increased or the interconnection width is widened by decreasing a space between the conversion element and the switching element or a space between the conversion element and the signal interconnection or drive interconnection in one pixel. However, in the above method, although the sensitivity is improved, because the space through which the light from the substrate backside passes is reduced, a necessary light irradiation time becomes lengthened from the substrate backside in order to compensate the decrease in sensitivity according to the space reduction. That is, the operation immediacy is lost.
In the above method, it is possible that a high-output light source is used to simply secure the operation immediacy and to achieve the maximum sensitivity. The high-output light source arranged in the backside of the substrate emits the light not having the image information. However, the compact apparatus cannot be formed, and sometimes cost increase is induced.
When the light irradiation is performed from the substrate backside, the switching element such as a TFT is also irradiated with the light in addition to the conversion element. Therefore, there is a possibility that a switching function is lost in the switching element because the photoelectric conversion is also generated in the switching element which is of the semiconductor element.